The invention relates to a tire pressure regulating device for at least one tire of a utility vehicle, having a pneumatically pilot-controlled relay valve which performs compressed air loading of a working line which starts from a pressure source and leads to the tire, in accordance with a pneumatic pilot controller which includes an electropneumatic converter for converting an electrical actuation signal into a pneumatic pilot control signal, corresponding to a setpoint tire pressure, for the relay valve. Furthermore, the invention also relates to methods for inflating at least one tire of a utility vehicle with such a tire pressure regulating device.
The field of application of the invention extends predominantly to utility vehicles which are used under different travel route conditions such as paved roads, off-road, sand, marshy ground and the like. These conditions require the tire pressure to be adapted to different conditions of the underlying surface even during travel. Therefore, in the utility vehicles which are of interest here there is a tire inflation device which adapts the actual (ACT) tire pressure which is present in the tires of the utility vehicle to a setpoint (SETPOINT) tire pressure which is predefined depending on the conditions of the underlying surface. Such a tire inflation device is usually a component of a pneumatic system of the utility vehicle which can also comprise a pneumatic brake system and, if appropriate, a pneumatic suspension spring system.
Tire inflation devices which use an aerating valve or a venting valve with a high throughflow rate to perform compressed air loading of one or more tires can be found in the generally known prior art. Depending on the ACT tire pressure which is measured by use of sensor technology, a difference in pressure compared to a predefined desired SETPOINT value is determined, in order to adapt the tire pressure subsequently. A selection of the tire to be inflated from a multiplicity of tires of a vehicle is made here by way of selection valves which establish a connection between the tire to be inflated and the valve device. In most applications, the aerating valve is connected in series with the venting valve and the valves are actuated either manually or electrically.
DE 34 05 101 A1 discloses, in contrast with the above, a tire pressure regulating device which is of the generic type and which makes use of a relay valve for tire inflation. The tire inflation device consists of a valve system in which solenoid valves and relay valves are functionally connected to one another. In accordance with the switched position of a manual control switch, regulating functions, which bring about an increase or decrease in the tire pressure are executed for the predefinition of the setpoint values. When the tire pressure is lowered, the compressed air which flows out of the tire is diverted into the atmosphere via an air outlet of a relay valve which is directly connected to a wheel valve. The predefined setpoint values which are selected manually by the control switch are passed on via an electrical signal line to an electromagnetic converter which actuates the pneumatic pilot controller of the relay valve. Within the scope of this tire inflation device, a sensor for measuring the ACT tire pressure serves only for performing displays and is not a component of a closed-loop regulating circuit.
DE 31 05 037 A1 discloses a tire inflation device with a relay valve, in which electropneumatic pilot control valves are also actuated with a manual setpoint value predefining means. The ACT tire pressure is measured here by a flow sensor. The relay valve and a shut-off valve are connected downstream of a manually settable regulating valve. The measuring principle of such a tire inflation device is represented by way of flow sensors which are arranged downstream of the relay valve in the supply line. With such a technical solution, differences in setpoint value can be compensated extremely promptly by the mechanical regulating components and they require a plurality of approximation steps.
DE 10 2012 008 002 A1 discloses a tire inflation device with a relay valve which is also subject to mechanical regulation. The aerating valve and venting valve which actuate the relay valve are themselves also pneumatically pilot-controlled. In this technical solution, the tire pressure circuit of a multi-circuit compressed air supply system of a utility vehicle is preferably to be supplied with compressed air.
The object of the present invention is to provide a tire inflation device using a pneumatically pilot-controlled relay valve for high through flows, which tire inflation device compensates quickly and precisely for a control error between a measured ACT tire pressure and a predefined SETPOINT tire pressure.
The object is achieved on the basis of a tire pressure regulating device for at least one tire of a utility vehicle, having a relay valve which performs compressed air loading or compressed air venting of a working line which starts from a pressure source and leads to the tire, in accordance with a pneumatic pilot controller which comprises an electropneumatic converter for converting an electrical actuation signal into a pneumatic pilot control signal, corresponding to the SETPOINT tire pressure, for the relay valve. The converter has an electropneumatic aerating valve and an electropneumatic venting valve for predefining pneumatic signal values for increasing or reducing the tire pressure.
In terms of process technology, the object is achieved by a method for regulating the pressure of at least one tire of a utility vehicle, using a relay valve with which compressed air loading or compressed air venting of a working line which starts from a pressure source and leads to the tire is performed in accordance with a pneumatic pilot controller with which an electrical actuation signal is converted, using an electropneumatic converter integrated therein, into a pneumatic pilot control signal, corresponding to the SETPOINT tire pressure, for the relay valve. The pneumatic pilot control signal corresponds to the SETPOINT tire pressure or is predefined as a function of the characteristic of the relay valve in proportion to the SETPOINT tire pressure.
The object is also achieved by a method for regulating the pressure of at least one tire of a utility vehicle, using a relay valve with which compressed air loading or compressed air venting of a working line which starts from a pressure source and leads to the tire is performed in accordance with a pneumatic pilot controller with which an electrical actuation signal is converted, using an electromagnetic converter integrated therein, into a pneumatic pilot control signal, corresponding to the SETPOINT tire pressure, for the relay valve. In the event of a low ACT tire pressure and/or high SETPOINT tire pressure in an initial phase of the aeration which is initiated as a result thereof, the control unit predefines a higher pressure than the SETPOINT tire pressure in order to accelerate the aeration, and/or in the event of a high ACT tire pressure and/or low SETPOINT tire pressure at the start of the venting which is initiated as a result thereof, the lowest possible pressure is predefined by means of the switch-off pressure of the wheel valve in order to accelerate the venting.
The invention includes the technical teaching that the converter has an electropneumatic aerating valve and an electropneumatic venting valve for predefining pneumatic signal values for increasing or reducing the tire pressure. It is preferably provided here that a pressure sensor, which is arranged on the working-line side of the relay valve, measures the profile of the tire pressure and passes on the measurement signal continuously to an electronic control unit for resetting to the predefined SETPOINT tire pressure, for which purpose either the aerating valve or the venting valve is electrically actuated, or both valves are held in the closed state.
The advantage of the solution according to the invention lies, in particular, in the fact that as a result of the continuous closed-loop regulation which is provided it is possible to react quickly to a control error which is to be compensated. Continuous monitoring of setpoint pressure differences which are to be compensated takes place by the continuous monitoring process of the tire pressure. No incremental aerating or venting phases are necessary in order to achieve a setting to the desired SETPOINT tire pressure at the end of the regulating process. The solution according to the invention sets a new pressure value on request, that is to say aerates, if a relatively high SETPOINT tire pressure is required, and vents if a relatively low tire pressure is required. Otherwise, the pilot controller is shut off. In this context, the ACT tire pressure is not measured directly by means of a pressure sensor arranged at the tire but instead the working pressure, which exits on the output side of the relay valve is measured in an analogous fashion in the working line leading to the tire.
The SETPOINT value for aeration or venting can be modified continuously during the aeration or venting with the electronically actuated regulating valve in order to reduce the time required for necessary compensation of the tire pressure.
According to one preferred embodiment of the invention, in the case of a plurality of tires of a utility vehicle, a respectively assigned wheel valve is provided in order to make a selection for one of the tires, for which necessary tire aeration or tire venting has to be carried out. As a result, a single tire inflation device, which adapts, according to requirements, the SETPOINT tire pressure for a plurality of tires connected thereto, is used for a plurality of tires.
The electropneumatic aerating valve and venting valve which predefine the desired control pressure of the relay valve through alternating actuation by the control unit are preferably embodied as monostable electropneumatic 2/2-way valves. As a result, reliable pilot control of the relay valve is achieved with low expenditure in terms of technical equipment.
The tire inflation device of the type described above is preferably actuated by the control unit in such a way that in the event of an excessively low tire pressure at the start of the aeration which initiated as a result thereof, at first a higher pressure than the SETPOINT tire pressure is predefined in order to accelerate the aeration. Conversely, in the event of an excessively high tire pressure the control unit can also predefine, at the start of the venting initiated as a result thereof, the lowest possible pressure above the shut-off pressure of the wheel valve in order to accelerate the venting. The same can also be achieved by an initial offset with respect to the actuation signal of the regulating device. The initial increase or decrease with respect to the SETPOINT tire pressure which is to be set or the control error which represents the manipulated value can be predefined on the basis of a characteristic curve which is stored in the control unit or formed thereby. The preferably linear characteristic curve ensures in the case of aeration that the predefined SETPOINT value drops continuously during the aeration. At the end of the aeration, the SETPOINT tire pressure is then reached. This is also implemented in an analogous fashion for venting.
According to a further measure which improves the invention, the control unit performs signal processing of both the tire pressure measured with the pressure sensor and further measurement signals, originating from the on-board pneumatic system, such as for example the current external temperature, the operating state of the vehicle engine or the current supply pressure value, for determining the pneumatic pilot control signal. An inflation time of the tire is calculated on the basis thereof, in order to carry out the aeration of the tire in the calculated time period. In addition, after modification of the tire pressure and of the further measurement signals of the on-board pneumatic system the electronic control unit can also newly calculate the inflation time, in order to be able to perform dynamic adaptation.
According to another preferred aspect of the invention, the electronic control unit prevents or interrupts the aeration if evaluation of the further measurement signals of the on-board pneumatic system reveals that the execution of a higher priority basic function of the on-board pneumatic system from the compressed air requirement of the tire inflation would be jeopardized. Therefore, the tire pressure regulation can be carried out with the same pneumatic system which, for example, also carries out the vehicle braking which is more important in terms of safety technology, without adversely affecting the function thereof.
The increasing of the aeration or the decreasing of the venting of the tire is preferably stopped by the control unit if the ACT tire pressure which is measured by the pressure sensor has reached at least 90% of the SETPOINT tire pressure. Best loading is carried on by means of the inertias present in the system. As a result, the SETPOINT tire pressure is not exceeded, which would immediately trigger venting of the tire as a result of the system oscillations generated thereby. This permits the SETPOINT value to be achieved in a targeted fashion.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.